Get rid of a redundant inline function.
Silence a warning for an unused function.
Delete a few unused local variables.
Add a virtual destructor to JSObject.

No virtual destructor for polymorphic types is bad!
Avoid a few signed/unsigned comparison warnings.
Enable -Wall and -Wextra for regsgen2.
Include <sys/types.h> to get ssize_t in regsgen2.

This unbreaks regsgen2 build on Mac OS.
Disable PlatformMain on windows (not supported).